1. Field of the Invention
This invention relates to earth boring bits, especially those having rolling cutters supported upon lubricated bearing shafts. The improvement relates specifically to the bearings in such bits.
2. Description of the Prior Art
The commercially successful earth boring bit used for drilling oil and gas wells has a body typically formed of three identical sections, each with a cantilevered bearing shaft that supports a rotatable cutter. An example of one version may be seen with reference to Bruce H. Burr, U.S. Pat. No. 4,516,641.
Here, the bearing is of the "journal" type, meaning that there are no rollers to support the load between the shaft and the cutter. The journal bearing has proved superior in most oil and gas well drilling environments since the inception of the successful bearing and seal system shown in U.S. patent of Edward M. Galle, No. 3,397,928.
In such bits there is often a high unit stress loading imposed on the journal bearing shaft by the corner region of the opposed seal ring groove in the cutter. The hard surface of the heat treated journal bearing surface sometimes cracks and spalls when subjected to sustained high unit loading imposed by the cutter, especially opposite the corner of the seal groove. This condition has been observed in bits sealed with O-rings and has become more prevalent in bits sealed with the improved metal face seals of Pat. No. 4,516,641.
There are also high unit stress loadings imposed on the radial thrust bearing surfaces used to resist the outward thrusts of the cutters during drilling. The cutters of a rock bit tend to wobble during drilling or assume a cocked position on the bearing shaft. This creates additional stresses on the thrust bearing.